Spent nuclear fuels are temporarily stored in nuclear power plant site. When a problem such as cracking of spent nuclear fuel assembly or cladding occurs or uranium that has not been separated during the reprocessing remains, it is necessary to treat it. The borosilicate glasses have been considered to vitrify whole spent nuclear fuel assembly. However, a large amount of Pb addition was necessary to oxidize metals in assembly to make them suitable for oxide glass vitrifcation. Furthermore, these borosilicate glasses need to be melted at high temperatures (> 1,400°C) when UO2 content is more than 20wt%. Iron phosphate glasses can be melted at a relatively low temperature (< 1,300°C) even with a similar UO2 addition. A composition of iron phosphate glass for immobilization of uranium oxide has been developed. The glasses have glass transition temperatures of ~555°C that are high enough to maintain its phase stability in geological repositories. The waste loading of UO2 in the glass is ~33.73wt%. Normalized elemental releases from the product consistency test were well below the US regulation of 2 g/m2. Nuclear criticality safety and heat generation in deep geological repositories were calculated using MCNP and computational fluid dynamics simulation, respectively. The glass had effective neutron multiplication factor (keff) of 0.755, which is smaller than the nuclear- criticality safety regulation of 0.95. Surface temperature of the disposal canister is expected to lower than the limit temperature (< 100°C). Most of the U in the glass is in the 4+state, which is more chemically durable than the 6+state. As a result of long-term dissolution experiment, chemically-durable uranium pyrophosphate (UP2O7) crystals were formed.

Among the fuel cell electrolyte candidates in the intermediate temperature range, glass materials show stable physical properties and are also expected to have higher ion conductivity than crystalline materials. In particular, phosphate glass has a high mobility of protons since such a structure maintains a hydrogen bond network that leads to high proton conductivity. Recently, defects like volatilization of phosphorus and destruction of the bonding structure have remarkably improved with introduction of cations, such as Zr4+ and Nb5+, into phosphate. In particular, niobium has proton conductivity on the surface because of higher surface acidity. It can also retain phosphorus content during heat treatment and improve chemical stability by bonding with phosphorus. In this study, we fabricate niobium phosphate glass thin films through sol-gel processing, and we report the chemical stability and electrical properties. The existence of the hydroxyl group in the phosphate is confirmed and found to be preserved at the intermediate temperature region of 150-450 oC.

Optical characteristics and structural changes depending on CuO content in phosphate glasses that are used in near-infrared (near-IR) filters were investigated. With phosphate glasses that contain 1-9 mol% CuO, changes in optical transmittance, optical absorption, and color coordinate were measured with a UV-VIS spectrophotometer. An XPS (X-ray photoelectron spectroscopy) analysis was performed to determine valence of copper ion that influences optical characteristics in near-IR filter glasses. Structural changes in glasses depending on CuO content were also analyzed by FT-IR (Fourier transform infrared) and Raman spectrophotometers. From the UV-VIS spectrophotometer results, strong absorption peaks at 220 & 900 nm were found and transmittance was decreased. The color coordinates of the glasses were shifted to the green color direction with CuO addition for increasing absorption of long wavelength range spectra, in spite of the amount of Cu2+, which gives a blue color to glasses, and which was increased in XPS results. Also, structural de-polymerization of glasses with CuO addition were found by FT-IR and Raman results.